1. Field of the Invention
The present invention relates to a heater block for heating a wafer, and more particularly, to a heater block which provides a wafer, disposed in a process chamber for PVD (physical vapor deposition), with the proper temperature enviromnent in a thermal process by supplying the wafer with uniform heat.
2. Discussion of the Related Art
A process for fabricating a semiconductor device is accompanied with a plurality of steps requiring high temperature for effecting oxidation, deposition, diffusion and the like.
The heating means for these thermal processes are set up in the processing chamber where the PVD process, for example, is carried out. Thus, heat is transferred to a wafer by transforming electrical energy into thermal energy in the use of a heating device such as a hot-wire. FIG. 1 shows a plan view of a heater block according to the prior art, and FIG. 2 shows a cross-sectional view taken along line I-I' of FIG. 1.
As shown in FIG. 1 and FIG. 2, the heater block comprises a body 100, a bellows 116, a power supply 103, a gas line 108, a controller 101 for checking the temperature and a clamp ring 112. The body 100 includes a heated element 106 wrapped with a hot wire 104 and a wafer support 102 for conveying the heat generated from the heated element 106 to the wafer support 102, wherein the wafer support 102 is located on the upper part of the body 100. The bellows 116 drives the body 100 in the upward and downward direction to position the body in a suitable location. The power supply 103 electrically connected to the hot-wire 104 selectively applies or cuts off electricity to the hot-wire 104 by turning the power on or off. The controller 101 monitors and controls the temperature of the wafer support 102. The clamp ring 112 is utilized to fix the wafer 110 to the wafer support 102.
The heater block according to a prior art is mounted on the lower part of the process chamber not shown in the drawings, and a gas supply pipe is installed at the upper part of the process chamber with an exhaust pipe being located at the lower part of the process chamber. Accordingly, while the processing gas is supplied to the inside of the processing chamber from the gas supply pipe, thermal processing such as deposition, diffusion and the like on the wafer heated by the heater block proceeds in accordance with the prior art. By-products from the process are exhausted through the exhaust pipe. The inside of the process chamber is constantly maintained at a pressure of 3 to 8 mTorr during the thermal process.
The procedure of heating the wafer with a heater block according to the prior art is a follows. To the heated element 106 is transferred the heat which is generated from the hot-wire 104 coruected to a power source when the power supply 103 is turned to the "on" position. The heated element 106 is made of a ceramic material and belongs to the body 100 under the wafer support 102 and is surrounded spirally by the hot-wire 104.
The heat transmitted from the heated element 106 preheats the wafer support 102 controlled by the controller 101 for maintaining the proper temperature in the thermal process. Once the wafer support is preheated to the proper temperature, a wafer 110 is mounted on the wafer support 102 by a transporting means, such as a robot arm, etc. Then the wafer support 102 is moved to a suitable level by the bellows 116 connected to the body 100.
Gas is supplied to the reverse face of the wafer 110 on which no device is being formed, wherein the gas line 108 is tunneled through the wafer support 102 and is connected to the discharge hole 118 formed in the wafer support 102 for carrying gas from the center to the ends of the wafer through the hole 118. The gas supplied through the gas line 108 is identical to the process gas supplied from the gas supply pipe formed in the process chamber, thereby heating the reverse face of the wafer as well as the heated element 106. This gas supply also contributes to the thermal process of diffusion, deposition, etc. on the wafer 110 together with the process gas which is supplied through the gas supply pipe. The gas supplied through the gas line 108 and the gas supply pipe is an inert gas, e.g., Ar. The gas introduced through the gas line 108 is maintained at a constant pressure as it contracts the reverse face of the wafer. The wafer 110 is fixed to the wafer support 102 by means of a clamp ring which clamps the top-side of the wafer to the support 102, while the pressurized gas is supplied during the thermal process.
As only one controller for monitoring the temperature is installed for the heated clement for heating the wafer support of the prior art heater block, a temperature difference may occur due to the impossibility of controlling each section of the wafer support from the center to the extremities, particularly if the hot-wire wrapped along the heated clement becomes broken or is weakened in its function.
Accordingly, there is a problem that an uneven distribution of temperature along the wafer is caused during the thermal process by the inability of the controller to control the temperature difference throughout the entire wafer. Moreover, the device is contaminated at the contact area between the wafer and the clamp ring due to particles that attach to or are introduced by the clamp ring itself.